1. Field of the Invention
The present invention relates generally to tape guidance devices and, more particularly, to a pneumatically controlled and compliant tape guidance mechanism.
2. Related Art
Recording data on magnetic tape media requires precise alignment of the media to the read/write head. This alignment is most commonly achieved by mechanically biasing the tape media against a reference edge with some form of spring loaded guides.
One conventional technique which applies the biasing load to the edge of the tape media employs mobile flat springs which contact the edge of the tape. Mobile flat springs are flexible, finger-like extensions which have one end secured in a stationary position and the other end unsecured and extending flexibly from the base.
Referring to FIGS. 1A and 1B, a prior art tape guidance device utilizing such a technique is illustrated. As mentioned above, the device of FIGS. 1A and 1B maintains pressure on the top edge 103 of tape media 102 with a mechanically induced bias, forcing it to maintain contact with reference edge 104 with its bottom edge 105. FIG. 1A illustrates the prior art device without magnetic tape media present. FIG. 1B illustrates the flat spring 106 applying pressure to tape media 102. The tape media 102 travels along what is referred to in the art as an "air bearing." Air bearing 112 supplies a cushion of air along which the tape media 102 travels. This cushion of air causes the tape 102 to travel past the air bearing 112 at a certain distance 101 away from air bearing 112. This distance 101 is referred to as the "tape flying height."
One of the disadvantages with this conventional approach is that the accuracy of the biasing load which is applied to the tape media 102 is determined by the flatness of the steel spring 106. The flatness of the spring controls some of the spring's final tape edge loading. Typically, the tolerance of the spring flatness can be held within 0.005 inches. This in turn causes large variations in the tape edge loading. This also results in less control over the amount of force applied to the tape edge and generates more debris than may be necessary due to the increased wear on the contacting components.
In addition, as shown in FIG. 1B, the flat spring 106 is bent when the tape 102 is present. This results in a non-perpendicular application of force to the top edge 103 of tape 102. As a result, the control over the tape media is reduced, since the load which is applied to the tape is reduced according to the angle at which it is applied. In addition, tape flying height 101 may be altered. It may be unintentionally increased if the guide button 108 pushes the tape media 102 away from the air bearing 112 or the tape flying height may be reduced if the guide button 108 pushes the tape media 102 towards the air bearing 112. In addition, this non-perpendicular force may alternate among multiple guide buttons should more than one be used.
Recently, there has been a great demand for increasing the amount of data which is written to or retrieved from the tape media 102. To satisfy this requirement without changing the size of the tape, the thickness and width of the tapes are reduced so as to increase the amount of tape accumulated on a single reel. However, reduction in the thickness of the tape greatly reduces its strength. In addition, the speed at which the read/write heads are capable of writing and retrieving information has also increased. As a result, control over the bias loading which is applied to the tape to maintain it against its reference edge has become even more critical to prevent damage from occurring to the tape.
These advances have identified additional problems with the conventional techniques: the sensitivity of the guidance device and the inability to adjust the biasing according to the application. For example, when changing the tape media 102 from a standard film (1 mil thick) to thin film (0.5 mil thick), a reduction in tape edge load would reduce tape wear. This cannot be accomplished with the conventional techniques without removing the tape media 102 and changing the flat spring 106 and guide button 108.
Another drawback of the conventional techniques described above is that the guide buttons 108 may roll along the axis of flat spring 106. This also reduces the loading control over the tape guide mechanism. In addition, as the guide buttons 108 `roll` along the axis of the spring, they introduce vibrations into the tape media 102. These vibrations result in shock waves which travel along the length of the tape media 102. Excessive vibrations can result in read and write errors at the read/write head. In addition, flat spring 106 may generate resonant vibrations at certain media speeds. Due to the flexible nature of the flat springs, these vibrations can cause the problems discussed above.
Another conventional tape guidance technique applies the biasing load to the edge of the tape media without the aid of guide button 108. Though this reduces the assembly costs, the steel spring causes more wear to occur to the tape media 102 than the ceramic guide buttons which are used in the above conventional technique. It also does not solve the problem of poor loading control.
What is needed is a tape guide device which can provide accurate tape edge loading. This tape edge loading must be applied at right angles to the media. In addition, the tape guide mechanism must be able to change the biasing load easily to accommodate different types of tape media.